Since antiquity, a multiplicity of measuring apparatuses have been known for recording properties of defined points in a measuring environment, in particular of spatial data. The location of a measuring device together with any reference points present, and direction, distance and angle to targets and measuring points, are recorded as standard spatial data.
A generally known example of such measuring apparatuses is the theodolite. An overview of geodetic measuring apparatuses of the prior art is provided by “Elektronische Entfernungs- und Richtungsmessung” [Electronic distance and direction measurement] by R. Joeckel and M. Stober, 4th edition, Verlag Konrad Wittwer, Stuttgart 1999 and “Electronic Distance Measurement” by J. M. Rüeger, 4th edition, Springer-Verlag, Berlin, Heidelberg 1996.
For controlling the measuring process, devices with camera/screen combinations which permit ergonomically advantageous use are also increasingly being used in addition to systems having an eyepiece. In addition, target identification or target tracking and hence facilitation and automation of the surveying process can be effected by the recording of an optical image.
Thus, for example, EP 1 314 959 and WO 2004/036145 disclose geodetic measuring devices having an electronic display and control apparatus, which permit screen-based operation.
In the two-dimensional representation of the optical image, it is possible to specify the points to which a measurement, i.e. the determination of distance and/or angle is made. On the basis of the image, targets can be identified and tracked by image processing methods, so that automated surveying is possible on this basis.
However, this image has no depth information at all, so that the image processing methods are reliant on appropriate preliminary information, image-recording conditions, such as, for example, the pre-alignment of a target plate, or image properties, such as, for example, brightness and contrast. The possibilities for target identification and tracking are limited by the purely visual capture. In particular, optical ambiguities as occur, for example, in the case of curved surfaces cannot be resolved. Thus, in a frontal recording under unfavourable light conditions, a disc and a sphere appear as an identical image in both cases.
The recording of purely visual images thus limits the control and automation of measuring processes in terms of the environmental conditions and target geometries.
For the production of topographies as static images with depth information, images of the Earth's surface or a celestial body are recorded from at least two different angles in aerial photogrammetry during a camera flight or a recording movement, from which images height information, for example for the preparation of map material, can be calculated on the basis of the collinearity relationship. In modern implementations of this method, photographs are digitized by scanning for electronic further processing or are digitally recorded during the flight itself.
EP 1 418 401 discloses a method and an apparatus for aerial or space photogrammetry, in which distance measurements to sampling points are additionally carried out using laser beams of a laser rangefinder during a camera flight with an aircraft for recording images which can be used in photogrammetry. The distance measurements are recorded in each case for a set of image points and later used as constraints for the preparation of a topography of the surface. Recorded distance measurements can moreover be used for optimizing the recording and flight parameters.
During the production of aerial images, preferably using a multiline sensor camera, distance measurements to sampling points which in each case are coordinated with a set of at least one image point are additionally carried out here for the recording of image points. These distance measurements are effected with laser rangefinders.
An alternative to conventional photogrammetry has arisen through the direct distance measurement from the aircraft to individual points by means of laser-based distance measurement (LIDAR). However, this method is not capable of providing further information to a comparable extent, for example in different spectral ranges. In addition, the image recording is effected by scanning, i.e. sequentially so that it is not suitable in applications for which rapid availability of image information is decisive.
Moreover, LIDAR systems having a scanning beam have disadvantages which result from the mechanical design. Either the entire device has to be moved over the visual region to be recorded or the beam guidance must be designed to be variable in an otherwise invariable apparatus. In addition to the expense of such mechanically and/or optically demanding or complex solutions, they generally have only a low scanning speed and in addition have a comparatively high energy consumption.
Systems which are based on sequential capture of additional depth or distance information moreover have problems of mechanical stability. Owing to the scanning movement and mechanical loads, for example due to vibration, the correlation of the distance measurements with the image points of the visual image is not ensured or is ensured only at additional expense.